1. Field of the Invention
The present invention relates to a multi-gear cluster for a bicycle, and more particularly to a multi-gear cluster having more than two gears of different diameters.
2. Description of the Related Art
Referring to FIG. 11 which shows a conventional multi-gear cluster, the prior art has provided various arrangements for facilitating a shifting movement of a chain 3 from a large gear 13 to an adjacent small gear 14 by e.g. cutting away top edges of some teeth 15, 16 of the large gear 13 or biasing these edges towards the small gear 14 (see the Japanese published patent gazette No. 56-3230).
Such conventional arrangements, however, have paid no consideration to the rotational phase relationship between the teeth 15, 16 of the large gear and the teeth of the small gear, so that the relationship remains irregular. Accordingly, in a change speed operation by shifting the chain between the gears, a portion of the chain 3 displaced (by means of a derailleur) towards the small gear 14 from a center of thickness of the large gear 13 fails to engage the teeth of the small gear 14, 16 and just rides over the top edges of the teeth at a shifting position C. Then, a perfect engagement between the chain 3 and the small gear 14 occurs only after the large gear 13 rotates for a few times. This not only impairs a smooth chain shifting operation but also, in a worse case, causes a complete derailment of the chain into the gap between the adjacent gear pair, thus completely disabling the entire bicycle drive system.
Taking the above-state of the art into consideration, the primary object of the present invention is to provide an improved multi-gear cluster for a bicycle which always permits a smooth and reliable chain shifting operation from the large gear to the small gear, the invention's cluster being superior also for being simple in construction and economical to manufacture.